In the process of cell culture, image observation of a culture state of microscopic cells has been carried out in the past mainly in laboratories of organization such as universities and institutes, by taking out the petri dish in which the culture is placed from a thermostatic chamber and observing the cells using a microscope.
Also, in order to extract the cells from image data obtained during cell culture, the threshold value has been calculated based on distribution of pixel values, and pixels equal to the threshold value and above or below have been extracted as the cell. However, the method using the above-mentioned threshold processing had a problem that the image turned out whitish, whereby detecting as if more cells exist than the actual amount. Consequently, in order to stably extract the cells without being influenced by color variation of the medium, light volume variation of the light source, difference in brightness between the central and peripheral areas of the image and the noise in the image, it has been fundamental to carry out a filtering process such as denoising, smoothing filter or edge enhancement.
In Patent Document 1, a method is described which monitors brightness variation in image data, generate a trigger signal at a specific threshold value, take images repeatedly with a camera, and obtains the added and averaged value of the images.
Patent Document 1: JP-A-2000-275539
Also, a technique for enabling observation of a motion state of individual cells by arranging a light source and a CCD camera facing each other placing an incubator therebetween, and imaging the cells in the incubator at an early stage of culture using the CCD camera is described in Non-patent Document 1.
Non-patent Document 1: Journal of Bioscience and Bioengineering Vo. 94, no. 4,351-356.2002 “Characterization of Cellular Motion Through Direct Observation of Individual Cells at Early Stage in Anchorage-Dependent Culture”.